The invention relates to a brush-commutated direct-current motor and also to a method for producing a brush-commutated direct-current motor.
A brush-commutated direct-current motor of this kind, as is known from GE 10 2011 082 543 A1 for example, comprises a stator which is fitted with a plurality of field poles, and a rotor which can rotate in relation to the stator about a rotation axis and which has a plurality of pole teeth. A plurality of windings are arranged on each pole tooth. A commutator which is arranged on the rotor has a plurality of lamellas, wherein each winding is connected to one of the lamellas by means of a first winding arm and is connected to another of the lamellas by means of a second winding arm. In addition, a plurality of short-circuiting links which each electrically connect two windings to one another and to this end are each arranged on at least two lamellas of the commutator are provided. The plurality of windings of the plurality of pole teeth are formed by a plurality of wire turns in this case, wherein each wire turn comprises one winding of each pole tooth and short-circuiting wires which connect the windings and is wound from a continuous wire.
In a direct-current motor, the number of pairs of brushes should usually correspond to half the number of (magnetic) field poles. If a direct-current motor has, for example, six field poles on the stator, three pairs of brushes, that is to say six brushes, are generally intended to be provided, said brushes being in sliding contact with the commutator and supplying current to the windings of the rotor in the desired manner. In this case, the brushes are arranged on the stator in a manner uniformly distributed about the rotation axis and have an alternating electrical polarity, so that a brush with a positive polarity is followed by a brush with a negative polarity and vice versa during operation of the direct-current motor. The brushes with a positive polarity and the brushes with a negative polarity are intended to be electrically connected to one another in this case, this requiring a comparatively large brush holder with a complicated design and circuitry.
For this reason, the direct-current motor which is known from DE 10 2011 082 543 A1 is provided with a plurality of short-circuiting links which are arranged on the rotor and each electrically short-circuit at least two lamellas of the commutator in order to bring individual lamellas to an identical potential. In this way, the number of pairs of brushes required can be reduced, and therefore, despite the use of, for example, six field poles, only one pair of brushes is required, without this having an adverse effect on the operating behavior of the direct-current motor.
Another arrangement of a direct-current motor, in which short-circuiting links for short-circuiting lamellas of a commutator are used, is known from U.S. Pat. No. 6,694,599 E1 in which the short-circuiting links are laid as wires separately between lamellas of the commutator.
JP 2004/088915 A2 discloses a direct-current motor in which the stator has six field poles, the rotor has eight teeth with in each case one winding and the commutator has twenty-four lamellas. In this case, the windings are connected to one another in such a way that they form a closed loop and are connected to one another in series. No short-circuiting links are provided or even required because the number of brushes is six, and therefore corresponds to the number of field poles.
In a brush-commutated direct-current motor which is known from WO 2011/121991 A1, a plurality of windings are provided on a rotor on pole teeth, wherein one winding is arranged on each tooth. In this case, the windings are connected to one another by means of short-circuiting links, wherein the short-circuiting links are laid through slots which are arranged between the pole teeth and said short-circuiting links short-circuit lamellas to which the windings are also connected.
If a plurality of windings are arranged on each pole tooth, as is provided in DE 10 2011 082 543 A1 for example, and the windings are wound in a plurality of wire turns using a single continuous wire or using a plurality of continuous wires, this has the result that each lamella is connected several times to one or more wires and therefore is fitted with at least as many wire connections as there are wire turns. If, for example, three wire turns are provided for arranging three windings on each pole tooth, each lamella is fitted with at least three wire connections which are formed, for example, by the continuous wire of each wire turn being suspended in a hook which is provided on the lamella.
Since each lamella has to be fitted with a plurality of wire connections, a connecting device, for example a hook, of corresponding dimensions which is able to accommodate a corresponding number of wire connections has to be provided on each lamella. This increases the installation space required in the motor, in particular in respect of its axial length, because installation space has to be reserved for the connecting devices.
If the wire turns are each in the form of closed turns in the case of which the turn begins at one lamella and also ends at the same lamella again, at least one lamella has to be fitted with even more wire connections than there are wire turns. When all wire turns are wound from a continuous wire, precisely one lamella to which the wire start and also the wire end are connected is produced, and therefore this lamella has to be fitted with a number of wire connections which corresponds to the number of wire turns plus one. If each wire turn is wound from a single continuous wire, a plurality of lamellas are fitted with a number of wire connections which corresponds to the number of turns plus one.
This further increases the installation space, in particular that which is to be provided in the axial direction.